1. Field of the Invention
The present invention relates to electromagnetic radiation concentrators for collecting electromagnetic radiation, and in particular, to a concentrator employing a plurality of concentrating means.
2. Description of Related Art
Various large electromagnetic radiation concentrators have been developed for use either as a solar energy collector, a solar furnace, a telescope and a radio telescope. Solar energy can be used for incineration, high heat applications and experiments and power production. Also, various electromagnetic radiation concentrators can be used for studying or listening for distant objects for celestial exploration.
A common solar energy collector employs a trough-like reflector with a parabolic or spherical profile. A pipe carrying a medium such as oil can be placed at the focus of the reflector. The temperatures that can be produced by this arrangement are limited. Theoretically, the size of the reflector can be increased indefinitely, but such an arrangement tends to have impractically tall walls and is very difficult to build with adequate accuracy.
An alternate solar collector employs a field of mirrors that can be adjusted to reflect sunlight onto an elevated receiver containing a medium such as molten salt, which is heated and used to produce power. These mirrors are flat reflectors. With the mirrors properly aimed, a high energy flux can be concentrated at a small region to raise the medium to very high temperatures. Basic geometric considerations limit the size of the field of mirrors. As more mirrors are added to the field, either the receiver or the mirrors must be successively raised in order to have a clear view for all mirrors. Otherwise, the farther back rows of mirrors would reflect sunlight onto the backs of the farther front rows of mirrors. In addition, the light being reflected onto the receiver becomes more and more distorted due to the angles between the mirrors and receiver becoming steeper. The light shining on the receiver becomes inefficiently spread over a relatively large surface area, similar to how the light from a flashlight that shines on a wall becomes elongated and distorted when you shine that flashlight at an angle to that wall.
Another electromagnetic radiation concentrator involves making a very large parabolic dish reflector. They either use one large solid concentrator or several small concentrators arranged next to one another to resemble one large concentrator. The dish reflector is constructed of whatever material is needed to reflect and concentrate the type of electromagnetic radiation desired. Like the trough reflectors, the size of the reflector can, theoretically, be increased indefinitely. However, the reflector becomes increasingly difficult to build, not to mention the difficulties in supporting and directing such a large structure to follow, e.g., the sun's movement across the sky.
In addition to the size limitations of the above systems, the amount of electromagnetic radiation concentration and the area over which it is concentrated is not adjustable. It remains fixed, once the system is built. Further, the concentrations produced are not in the form of a parallel beam. Such a beam would allow many additional uses including but not limited to: cutting and boring, space and other vehicle propulsion, and laser weaponry.
U.S. Pat. No 4,021,267 shows an apparatus for powering an array of photovoltaic cells. The light from a concentrating reflector is collimated via use of either a lens or a collimating mirror, (similar to a Cassegrain telescope) which then is sent through a prism in order to separate the light into a spectrum. The spectrum then falls on the array of photovoltaic cells. This device does not provide for any means of scaling up the system to gather light from a large area.
U.S. Pat. No. 5,613,768 shows an apparatus for generating parallel light. This arrangement employs a parabolic mirror that is shown in FIG. 5 shining onto an array of mirrors that, in turn, focus light onto a number of apertures that screen the light before it is reflected it again with another array of mirrors. This arrangement is primarily concerned with screening unwanted light from a lamp. It cannot concentrate incoming electromagnetic radiation into a beam.
U.S. Pat. No. 5,220,462 shows a diode glazing, designed to favor the passage of light in only one direction. This device has a series of parallel, semi-cylindrical surfaces that concentrate light through gaps in an array of mirrors. This reference does not discuss combining the light passing through these gaps into a compact beam.
U.S. Pat. No. 5,138,490 shows a grating and mirror for tailoring the intensity profile in a laser beam. The mirror has a convoluted surface, which is designed to reflect a divergent beam, and is therefore not designed as a light concentrator.
U.S. Pat. No. 5,237,170 shows a single reflector, but this disclosure does not reveal any means for scaling up the system to gather light from a large area.
See also U.S. Pat. Nos. 5,214,540; 5,331,470; 5,427,628; 5,631,770; 5,640,283; and 5,684,611.
Accordingly, there is a need for a practical and efficient electromagnetic radiation concentrator that can gather electromagnetic radiation over a relatively large area without size limitations and also produce a concentrated adjustable directed energy beam.